Modern wind turbines are commonly used to supply electricity into the electrical grid. Wind turbines of this kind generally comprise a rotor with a rotor hub and a plurality of blades. The rotor is set into rotation under the influence of the wind on the blades. The rotation of the rotor shaft either directly drives the generator rotor (“directly driven”) or through the use of a gearbox.
In the turbines using a gearbox, a slow speed shaft (which commonly is the rotor shaft) enters the gearbox. The rotation of the slow speed shaft is transformed through suitable gearing to rotation of a high speed shaft, which drives the generator. Lubricant (which commonly is oil, possibly with additives) is provided in the gearbox to reduce friction between the gears. This improves efficiency and reduces wear of the parts. An additional function of the lubricant is to dissolve particles and to prevent corrosion.
Lubricant is normally heated up by the heat that is generated by the contact between the gears in the gearbox. The lubricant thus needs to be cooled and is generally circulated through a circuit comprising a cooler or heat exchanger. A pump is used to pump the lubricant exiting the gearbox through the cooler and then back to the gearbox.
In direct-drive wind turbines, the rotor shaft directly drives a generator rotor. Lubrication in this kind of wind turbines may be needed e.g. for the rotor shaft bearings. Cooling of lubricant is generally also required in this case.
JP2007224879 discloses a yaw drive system comprising an electric motor for rotating a nacelle. A hydraulic pump, which is driven through a connection to the gearbox provides hydraulic fluid to a brake for locking the nacelle in its position.
EP 0 093 461 discloses a lubricating oil pump, which is coupled with the rotor shaft by means of a gear wheel drive. The lubricating oil pump supplies the lubricating oil through oil ducts to bearings in a cabinet. Cooling vanes for cooling the lubricating oil are provided on the outside of the cabinet.
Other prior art systems may typically comprise an oil-air heat exchanger for cooling the lubricant. Cooling air is provided by a fan driven by an electric motor. The pump for pumping lubricant through the hydraulic circuit may be driven by another electric motor or a hydraulic motor.
Electrical motors have the disadvantage that they are big and heavy. Additionally, they require electrical supply and controls and additional protection systems. Hydraulically driven motors need hydraulic power to be generated from a hydraulic power pack from electricity. Especially in modern, large wind turbines, the motors that are required may be heavy and expensive.
An alternative, at least for the pump for pumping lubricant through the lubrication circuit, may be to use a power-take-off from the gearbox. However, such a power-take-off is relatively complex and expensive.
There thus exists a need for a cost-efficient wind turbine lubrication circuit.